A pigment dispersion method is used in one of the methods for preparing a color filter used for a liquid crystal display device, a solid-state imaging device, or the like. Examples of the pigment dispersion method may include a method of producing a color filter using a photolithographic method using a colored radiation-sensitive composition having a pigment dispersed in various photosensitive compositions. This method has been widely used as a method suitable for preparing a color filter for a large-screen high-definition color display since it is stable against light or heat as a result of the use of a pigment, and further, can ensure sufficiently positional precision for patterning according to a photolithographic method.
When a color filter is prepared by the pigment dispersion method, a radiation-sensitive composition is applied onto a substrate using a spin coater, a roll coater, or the like, and dried to form a coating film, and the colored image pixels are formed by pattern exposure and development of the coating film. This operation for respective colors can be repeated to prepare a color filter.
However, the color filter for a solid-state imaging device has been required to have high precision in recent years, and it has been difficult to further improve the resolution according to the conventional pigment dispersion system. Further, the pigment dispersion method is not suitable for applications requiring fine patterning such as a solid-state imaging device because of the occurrence of color unevenness due to coarse particles of the pigment, or the like.
In order to achieve the above-mentioned high resolution, there has been conventionally proposed the use of a dye as a dye (see, for example, Japanese Patent Application Laid-Open (JP-A) 6-75375). However, it could be seen that a curable composition containing the dye has further new problems as follows.
(1) The dye is generally inferior in terms of light-fastness and heat resistance, as compared with pigments.
(2) General coloring materials have a low solubility in an alkali aqueous solution or in an organic solvent (hereinafter also simply referred to as a solvent), and therefore, it is difficult to obtain a liquid-state curable composition having a desired spectrum.
(3) The dye exerts an interaction with other components in the curable composition, and accordingly, it is difficult to control the solubility (developability) of a cured portion and an uncured portion.
(4) If the molar absorption coefficient (ε) of the dye is low, it is necessary to add a large amount of the dye, for which the amount of other components such as a polymerizable compound (monomer), a binder, a photopolymerization initiator, and the like in the curable composition must be reduced, and problems occur where the curability of the composition, the heat resistance, the developability of the (un)cured portion, or the like would be reduced after curing.
Due to these problems, it has been difficult to form a colored pattern constituted on a fine thin film for a high precision color filter so far. Also, unlike a case of the applications for preparation of a semiconductor or the like, in the case of the applications for preparation of a color filter for a solid-state imaging device, for example, it is required that the film have a small thickness of 1 μm or less. Therefore, in order to obtain a desired absorption, it is necessary to add a large amount of the coloring material into the curable composition, which results in the problem as described above.
Conventionally, a phthalocyanine dye has been widely used as a pigment in green or blue color filters. Further, its usefulness when it used as a dye has been also known (see, for example, JP-A No. 2002-14221, JP-A No. 2002-14222, and JP-A No. 2006-47497). However, in the case where a phthalocyanine is used, in order to satisfy the solubility in an organic solvent, various substituents should be introduced. As a result, the molecular weight increases, and therefore, in order to obtain a desired absorption, it is necessary to add a large amount of the coloring material into the curable composition, which results in the problem as described above. Accordingly, a dye which does not cause an increase in molecular weight and satisfies the solubility in an organic solvent is demanded.
Furthermore, conventionally, a dye has been required to have high fastness. Specifically, a colorant used in various applications is generally required to have the following properties in common. That is, it is necessary that the dye have preferable absorption characteristics in terms of color reproducibility, fastness under the environment condition for use, for example, good heat resistance, light-fastness, moisture resistance, or the like, and a high molar absorption coefficient, and be capable of being formed into a thin film.